The present invention relates to a composite structure for a bat.
The performance of a baseball or softball bat is determined by a number of factors such as weight, swing weight, ball rebound velocity, strength, and aerodynamics. The traditional metal or composite material bat is a single tubular structure with a hitting portion, a gripping portion, and a tapered portion connecting the two. The wall thickness can vary along its length to provide specific performance needs. The bat may be made from a number of materials such as aluminum, steel, titanium, and light weight composite materials.
The weight of a bat is a critical feature in determining performance. The lighter the bat weight, the easier it is to swing the bat resulting in higher swing speeds. Therefore, the lightest materials and designs are used to achieve these performance goals. The most popular high performance material for modern bat design is carbon fiber reinforced epoxy resin (CFE) because it has the highest strength and stiffness-to-weight ratio of any realistically affordable material. As a result, CFE can produce a very light weight bat with excellent strength as well as providing a variety of stiffnesses.
Another very important characteristic is how the ball rebounds off the face of the bat. A desired characteristic is to have the face of the bat deform and return during ball contact to increase the rebound velocity or coefficient of restitution (COR). This can be accomplished by producing the bat as a hollow structure, with the walls of the bat produced using a light weight metal or fiber reinforced composite material. However, care should be taken not to make the walls too thin and weak, because considerable hoop stress exists when the bat contacts the ball.
Another desirable feature in a bat is comfort. Striking the ball off the center region or “sweet spot” of the bat can be a painful experience due to the resulting torque (shock) and vibrations transmitted to the hands. All types of shock and vibration are magnified with a bat of a lighter weight, which doesn't have the sufficient mass or inertia to absorb the shock or damp the vibrations.
Another desirable feature in a bat is aerodynamics. However, aerodynamics have not been seriously considered in the past because most bats are restricted by their external geometry and bat diameter which determines aerodynamic drag.
The evolution of the modern bat over the past twenty years has focused on light weight, improving ball rebound velocity, comfort, improving strength, and aerodynamics. However, there has not been a bat that has all of the mentioned performance benefits.
An example of producing a bat out of light weight composite materials is U.S. Pat. No. 4,931,247 to Yeh who discloses a process of rolling up sheets of fibers impregnated with resin and placing in a mold and internally inflating using a bladder. This created a light weight product which was easier to swing.
A design to increase the Coefficient of Restitution (COR) of a bat is shown by U.S. Pat. No. 6,872,156 to Ogawa, et. al., who describes a bat with an exterior elastic sleeve in the hitting portion of the bat to improve ball rebound velocity. Other examples are U.S. Pat. Nos. 6,764,419 and 6,866,598 to Giannetti et. al., and U.S. Pat. No. to Buiatti, et. al., who describe a bat with a thin cylindrical outer wall, an internal cylindrical inner wall with material in between to improve the ball rebound velocity and to improve strength.
U.S. Pat. No. 6,808,464 to Nguyen discloses an improvement to the comfort of a composite bat by using elastomeric caps at the end of outer walls and internal walls to create a wood like feel and damp vibrations.
U.S. Pat. No. 6,383,101 to Eggiman, et. al., describes an insert or sleeve of a fiber reinforced composite material with fibers aligned circumferentially to obtain improved strength. Other examples of using composite materials to improve strength are disclosed by U.S. Pat. No. 6,723,012 to Sutherland who uses a three-dimensional fiber reinforcement architecture to improve durability, and U.S. Pat. No. 6,776,735 to Belanger, et. al., who use continuous fibers embedded in a resin to achieve superior strength over the traditional wood bats. Also, U.S. Pat. No. 6,761,653 to Higginbotham, et. al. combines a metal bat with an exterior fiber reinforced composite shell to improve strength.
There exists a continuing need for an improved bat system. In this regard, the present invention substantially fulfills this need.